If you live in North America, at some point in your life you need to explore the surreal landscapes that stripe from the American Southwest of the painted desert up north and east through the petrified forest and the moraines of Wisconsin and the craters of Canada. My favorite region is the canyonlands and the badlands where past floods carved the twisted landscape that has dried to a magnificent desert.

Trying to understand the weird beauty of this landscape has been a challenge to geologists but in a case of “oh, in retrospect that makes a world of sense”, researchers have pointed out a missing variable that makes everything a lot easier to understand.

According to new research in Proceedings of the National Academy of Sciences and led by Tamara Pico: the land we see today is at a level and a tilt that reflects its hot, dry, modern reality, but when those canyons formed, the landscape was tilted and weighted down by massive glaciers — glaciers that melted in canyon-forming megafloods.

I love this story for a lot of reasons. Here in the U.S. Midwest, we have random earthquakes that result from the land still rebounding from glaciers. The past crush of ice still affects us today. There are also ancient stories from myriad indigenous cultures that tell of past massive floods. This research connects our modern stories and reality with the ancient landscape.

In a press release on this paper, Pico’s results are summarized as follows: During the height of the last ice age, vast ice sheets covered much of North America. They began to melt about 20,000 years ago, and the Missoula megafloods occurred between 18,000 and 15,500 years ago. People have been looking at high water marks and trying to reconstruct the size of these floods, but all of the estimates are based on looking at the present-day topography. This paper shows that the ice age topography would have been different over broad scales due to the deformation of Earth’s crust by the weight of the ice sheets… During this period, the deformation of the Earth’s crust in response to the growing and shrinking of ice sheets would have changed the elevation of the topography by hundreds of meters.”

What we see today is shaped by the past, but it wasn’t shaped by just one thing. It was floods and the weight of ice, and to understand what we see, we really have to take into account all the forces. It’s obvious in retrospect but apparently way too easy to forget. And now we will remember: don’t look at the landscape as it is now but imagine where it was in the past when trying to understand what has happened in the past.

More Information

UCSC press release

“Glacial isostatic adjustment directed incision of the Channeled Scabland by Ice Age megafloods,”  Tamara Pico et al., 2022 February 22, PNAS